Diabetes mellitus is a chronic metabolic disorder caused by an inability of the pancreas to produce sufficient amounts of the hormone insulin, resulting in the decreased ability of the body to metabolize glucose. This failure leads to hyperglycemia, i.e. the presence of an excessive amount of glucose in the blood plasma. Persistent hyperglycemia and hypoinsulinemia have been associated with a variety of serious symptoms and life-threatening long-term complications such as dehydration, ketoacidosis, diabetic coma, cardiovascular diseases, chronic renal failure, retinal damage and nerve damages with the risk of amputation of extremities. Because restoration of endogenous insulin production is not yet possible, a permanent therapy is necessary which provides constant glycemic control in order to always maintain the level of blood glucose (BG) within normal limits. Such glycemic control is achieved by regularly supplying external insulin to the body of the patient to thereby reduce the elevated levels of blood glucose.
External biologic agents such as insulin can be administered as multiple daily injections of a mixture of rapid and intermediate-acting drugs via a hypodermic syringe. Improved glycemic control can be achieved by the so-called “intensive hormone” therapy which is based on multiple daily injections, including one or two injections per day of a long acting hormone for providing basal hormone and additional injections of rapidly acting hormone before each meal in an amount proportional to the size of the meal. Although traditional syringes have at least partly been replaced by insulin pens, the frequent injections are nevertheless very inconvenient for the patient, particularly those who are incapable of reliably self-administering injections. For some patients, substantial improvements in diabetes therapy have been achieved by the development of drug delivery devices, such as pumps, that relieve the patient of the need for syringes or drug pens and the need to administer multiple daily injections. Drug delivery devices can be constructed as an implantable device for subcutaneous arrangement or can be constructed as an external device with an infusion set for subcutaneous infusion to the patient via the transcutaneous insertion of a catheter, cannula or a transdermal drug transport such as through a patch.
Blood or interstitial analyte monitoring can be used to achieve acceptable glycemic control. The determination of blood glucose concentration can be performed by means of an episodic measuring device, such as a hand-held electronic meter that receives blood samples on enzyme-based test strips and calculates the blood glucose value based on an electrochemical reaction of the blood and the enzyme. Continuous glucose monitoring (CGM) using a sensor inserted into or implanted in the body can also be used.
Many patients use episodic measuring of blood glucose. This approach is straightforward but requires regular attention from the patient. Even patients using CGM and insulin pumps are generally required to check their blood-glucose readings throughout the day and consume sugars as necessary to forestall hypoglycemia. The required level of attention can be discouraging for some patients. Moreover, as glucose-monitoring and glucose-control systems become more complex, it can be difficult for some patients to effectively use their glucose meters or drug-delivery devices.
Besides glucose, there are other analytes of interest such as, for example, ketone or cholesterol, which can be monitored by a person with diabetes or other chronic diseases. It is believed that these analyte meters suffer from the same shortcomings as the glucose meter.